
I agree with Wise. I'm sure without the nightlock they could have found another way of attempting suicide in order to rebel, but the berries were a good thing for Collins to go with as they then served as a symbol - plus they would have killed Katniss & Peeta instantly. Had she gone with something else there would have been the possibility of one dying before the other, making the other the winner and having the capitol then intervene to save the winner from whatever mortal wound had been inflicted.